CB2

• Asexual reproduction


  Reproduction using just one parent, producing offspring that are clones (genetically identical)
• Asexual reproduction relies on mitosis
• Organisms that reproduce asexually

  • Strawberry plants
  • Potatoes
  • Aphids
• Asexual reproduction is much faster than sexual reproduction
• Sexual reproduction produces variation, asexual reproduction does not
• Normal cells only divide when they need to
• Changes in cells can turn them into cancer cells, which undergo uncontrollable cell division
• Rapid cell division produces growing lumps of cells called tumours that can damage the body and result in death
• Growth


  Increase in size as a result of an increase in number or size of cells
• Percentile growth charts


  Charts used to monitor growth in children by comparing measurements to a large population
• Cell differentiation changes less specialised cells into more specialised ones
• Red blood cell


  • No nucleus, allowing more space for red haemoglobin molecules
  • Large surface area, allowing oxygen to diffuse in and out more quickly
• Fat cell


  • Cytoplasm filled with large fat droplets, storing fat until the body needs energy
• Nerve cell (neurone)


  • Long fibre that carries electrical impulses around the body
  • Many connections to other neurones
• Muscle cell


  • Contains special contractile proteins that can shorten the cell
• Meristem


  Group of cells near the end of each shoot and root that allow plants to continue growing
• What are the stages of growing in plants?

  1. Cell Division

  2. Elongation

  3. Differentiation
• Cells in plant meristems divide rapidly by mitosis
• Root hair cells


  • Adapted to absorb water and mineral salts from the soil
• Xylem vessels


  • Long tubes formed from dead xylem cells, with thickened walls to withstand water pressure and tiny pores to allow water and mineral salts to enter and leave
• Plants need root hair cells and xylem vessels
• Stem cells


  Cells that can divide repeatedly over a long period to produce cells that then differentiate
• Plant stem cells can produce any kind of specialised cell throughout the plant's life
• Animal embryonic stem cells can produce any type of specialised cell, but adult stem cells are more limited
• Adult stem cells


  Stem cells in developed tissues that allow the tissues to grow and replace old or damaged cells
• Unspecialised


  Not specialised for a particular function
• Blood stem cells


  • Found in bone marrow, continue to divide throughout life to produce new blood cells
• Stem cells can be stimulated to produce the specialised cells needed and injected into the places they are needed
• Problems with using stem cells include them continuing to divide and causing cancer
• The brain and spinal cord form the central nervous system (CNS), which controls your body. Nerves make up the rest of the nervous system. This organ system allows all the parts of your body to communicate, using electrical signals called impulses.
• Anything your body is sensitive to, including changes inside your body and in your surroundings, is called a stimulus. Sense organs (such as eyes, ears and skin) contain receptor cells that detect stimuli. For example, skin contains receptor cells that detect the stimulus of temperature change.
• Receptor cells create impulses, which usually travel to the brain. The brain then processes this information and can send impulses to other parts of the body to cause something to happen (a response).
• The travelling, or transmission, of impulses is called neurotransmission and happens in neurones (nerve cells). Neurones have a cell body and long extensions to carry impulses.
• The device in photo A allows blind people to see ... with their tongues! The image from the camera is sent to a 'lollipop' that contains hundreds of small electrodes. Each electrode produces pulses of electricity depending on how much light is in that part of the image. By putting the lollipop on the tongue, the user can feel these pulses and build up an idea of basic shapes and movement. This allows some blind people to react and respond to visual stimuli.
• When the brain coordinates a response to a stimulus, impulses are sent to effectors and these carry out an action. Effectors include muscles and glands (e.g. sweat glands).
• One neurone meets another at a synapse, which contains a tiny gap. When an impulse reaches an axon terminal, a neurotransmitter substance is released into the gap. This is detected by the next neurone, which generates a new impulse. Synapses slow down neurotransmission. They are, however, useful because neurotransmitters are only released from axon terminals and so impulses only flow in one direction. They also allow many fresh impulses to be generated in many neurones connected to one neurone - the original impulse does not need to be split and lose 'strength'.
• If you touch a very hot object you need to pull your finger away very quickly to stop it burning you. You don't want to have to waste time thinking about this and so a reflex is used. Reflex actions are responses that are automatic, extremely quick and protect the body. They use neurone pathways called reflex arcs, which bypass the parts of the brain involved in processing information and so are quicker than responses that need processing.
• If you touch a hot object, receptor cells in the hand detect this. Impulses travel into a sensory neurone, and then into a relay neurone in the spinal cord. After this, the impulses pass to motor neurones, which cause muscles (the effectors) to move the hand quickly out of the way. This pathway is called a reflex arc, and it is shorter than if the impulses had to go to the brain to be processed. This means that the response is much quicker than usual. This means that the hand is moved away from the hot object as quickly as possible, meaning that there is less chance of it being burnt.
• This image was made by splicing together a photograph of a mother (aged 52) and her son (aged 30). It is one of a number of 'genetic portraits' created by Canadian graphic designer Ulric Collette to illustrate how closely members of the same family resemble one another. In this unit you will learn about the DNA code that produces our features and the processes that allow features to be passed on from parents to their offspring.
• What is the order of the cell cycle?


  1. Interphase
  2. Prophase
  3. Metaphase
  4. Anaphase
  5. Telophase
  6. Cytokinesis